1. Field of the Invention
The present invention relates to a photoconductive member which is sensitive to electromagnetic waves such as light (the light herein is in a broad sense including ultraviolet rays, visible rays, infrared rays, X-ray, .gamma.-rays, etc.).
2. Description of the Prior Art
Photoconductive materials forming photoconductive layers in solid-state image pickup devices and in image forming devices, e.g. electrophotographic image forming members and original-reading devices, are required to have characteristics such as high sensitivity, high S/N ratio [photo-current (Ip)/dark current (Ia)], absorption spectral characteristics fitting the spectrum of the electromagnetic waves to be irradiated, quick photoresponsiveness, desired dark resistivity, and safety to human body during use, and further in solid-state pickup devices, easiness of afterimage treatment in a given time. In particular the safety to human body during service is important to the photoconductive materials to be incorporated into electrophotographic appliances for office purposes.
A photoconductive material recently found which possess the above points is amorphous silicon (hereinafter designated as a-Si), which is described for Example, in German Pat. Offen. Nos. 2,746,967 and 2,855,718 as an electrophotographic image forming member and in German Pat. Offen. No. 2,933,411 as applicable to reading devices utilizing a photoelectric conversion type of reader.
However, the prior art photoconductive member having a photoconductive layer formed of a-Si still needs an overall improvement of characteristics including electrical, optical, and photoconductive properties such as dark resistivity, photosensitivity, and photoresponsiveness, environment resistances such as humidity resistance, and stability during passage of time.
For instance, when photoconductive members of a-Si type were used as electrophotographic image forming members, attempts in the past of simultaneous enhancements of photosensitivity and dark resistance often brought about undesirable effects such that; residual potential was frequently observed during service; fatigue accumulated in repeated operations continued for long hours and this led to the appearance of a so-called ghost phenomenon that is the occurrence of an afterimage; and the responsiveness gradually deteriorated in high-speed repeated operations.
In addition, a-Si has a relatively low absorption coefficient for light waves longer than short-side visible light waves. Accordingly, the prior art photoconductive layer made of a-Si is ineffective in utilizing the energy of semiconductor lasers which are in practical use or the longer-wave energy of halogen lamps or fluorescent lamps, when these light sources are used for the irradiation thereof. This is one of the still remaining problems to solve.
Meanwhile, when a large portion of the illuminating light arrives at the substrate (support) of a photoconductive member without being absorbed in the photoconductive layer, light interference due to multiple reflection will take place in the photoconductive layer if the substrate has a high reflectance for the light incident thereupon through the photoconductive layer. This interference is a factor in causing the "unfocused image".
As the irradiation spot is made smaller for the purpose of improving the resolution, the above effect becomes more remarkable. This is a significant problem in particular when a semiconductor laser is employed as a light source.
Moreover, when the photoconductive layer is constituted of a-Si, hydrogen atoms or halogen atoms such as fluorine or chlorine atoms are usually incorporated thereinto for the purpose of improving the electrical and photoconductive properties, and boron atoms, phosphorus atoms, or some other atoms are also incorporated for the purpose of controlling the conduction type, where a problem arises occasionally in the electrical or photoconductive properties of the resulting layer depending upon the manner of the incorporation. For instance, the problem is that photocarriers produced by light irradiation in the resulting photoconductive layer are inadequate in lifetime in this layer or that the injection of electric charge from the substrate side in the dark area is not sufficiently impeded.
Furthermore, in the formation of the photoconductive layer thicker than ten and several m.mu., a phenomenon such as the lifting or peeling of the layer from the substrate or cracking in the layer is liable to develop with the time of leaving the product in the air after withdrawal thereof from the vapor-deposition chamber used for the layer formation. This phenomenon is remarkable in particular when the substrate is of a drum type commonly used in the field of electrophotography. Thus the photoconductive member involves problems to be solved with respect to durability.
Accordingly, it is necessary to improve characteristics of a-Si material itself and, on the other hand, to design photoconductive members employing it so as to solve all the problems noted above.
The present invention has been made in view of the above various problems. That is, as a result of intensive studies continued from the general point of view on the adaptability and utility of a-Si for photoconductive members used in electrophotographic image forming members, solid-state image pickup devices, readout devices, etc., it has been found that a photoconductive member provided, according to a specified design as will be described later, with a photoconductive light receiving layer which comprises an amorphous material containing a silicon atom (Si)-germanium atom (Ge) mixture as matrix and hydrogen atoms (H) or/and halogen atoms (X), i.e. a so-called hydrogenated amorphous silicon-germanium, halogenated amorphous silicon-germanium, or halogen-containing hydrogenated amorphous silicon-germanium (hereinafter these materials are generically designated as "a-SiGe(H,X)"), exhibits excellent characteristics for practical use, supasses the prior art photoconductive member in all respects, and in particular has excellent characteristics suitable for electrophotography and exhibits an absorption spectrum favorable for longer waves of light. Based on this finding, the invention has been accomplished.